My experience is that slowly increasing SWR is from a component heating up, usually an inductor in a tuner or balun. You don't see it with lower power. Ferrite cores change their inductance radically as they heat up near their Curie temperature. If they get to their Curie temperature, they lost their magnetic properties. As the SWR goes up, they get even hotter, SWR goes up more and if you don't stop transmitting, they will fail.
All SWRs with the same number are not equal in terms of losses in a tuner or balun. As Victor described, when the load it highly reactive, there are more losses in the tuner or balun. If you have an IR thermometer, you should be able to point it at inductors and see what is getting hot. I've got a horizontal loop that is slightly too small for 160. I have an added shunt inductor in the line to allow my tuner to tune it, but the inductor, which is on a 2.4" core still gets hot. Most tuners have smaller inductors than that. My home built balun also has 2.4" cores. Many baluns use smaller cores. 73, Mark W7MLG On Fri, Apr 10, 2020 at 7:16 AM Victor Rosenthal 4X6GP <[email protected]> wrote: > I would be more likely to suspect something after the KPA500, such as > the tuner or a balun. I've experienced significant balun heating, > especially when using a balun other than a straight-through 1:1 balun, > or when the load is highly reactive. Balun power ratings assume a > non-reactive load. > > 73, > Victor, 4X6GP > Rehovot, Israel > Formerly K2VCO > CWops no. 5 > http://www.qsl.net/k2vco/ > On 10/04/2020 14:26, Alan - G4GNX wrote: > > > > I have a strange fault a couple of times recently, where the SWR starts > > to increase during the time of a single 'over'. I've been using the K3S > > set at 100W out, via the KPA500 (in standby) and the KAT500 tuner, > > without any problem, but after I've switched the linear to Operate and > > driving it to 200W, the SWR creeps up. I don't think it's an antenna > > issue, but a possible heat problem with the KPA500. I watched the > > temperature display on the KPA500 and initially on Standby it shows > > about 38 degrees C. After transmitting at 200W the temperature slowly > > rises above 60 degrees C, but the fan doesn't cut in. Does anyone know > > if this is normal behavior and what temperatures I should expect to see? > > I have tested the fan via the Menu function and it works as expected. > > > > 73, > > > > Alan. G4GNX > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[email protected] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > Message delivered to [email protected] > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
